In recent years, there is a requirement to improve the heat insulating properties of foamed heat insulation materials by reducing their thermal conductivity from the standpoint of energy-saving. At the same time, it is a very important theme to reduce the quantity of fluorocarbons used as a foaming agent and thereby to contribute to the improvement of environmental problems caused by fluorocarbons such as the destruction of the ozone layer, the rise in atmospheric temperature on the earth, etc.
For this reason, in the production of rigid urethane foams as typical foamed heat insulation material, various improvements are being attempted with regard to main starting materials such as polyol and organic polyisocyanate, as well as assistant raw materials such as foam stabilizer, catalyst and foaming agent. In order to reduce the thermal conductivity of rigid urethane foams, it is fundamentally important to improve the gas thermal conductivity of a gas component in foams, and it has been considered to be particularly an effective measure to use trichlorofluoromethane (hereinafter referred to as R-11) as a foaming agent and to fill the bubbles of foams with R-11 gas. However, on the other hand, in order to reduce the quantity of used fluorocarbons from the viewpoint of environmental pollution problems caused by fluorocarbons, etc., it is also possible to replace the foaming agent partially with carbon dioxide generated by reaction of a organic polyisocyanate and water. In such a construction, however, the carbon dioxide remains in the foams of the foamed heat insulation material and thereby the heat insulating performance of the foamed heat insulation material is deteriorated.
As an attempt to solve this problem, for example, a method of removing impurity gas components by the use of an adsorbent was proposed in Japanese Patent Application Kokai (Laid-Open) No. 57-49628. That is, the characteristic feature of this method consisted in previously mixing an adsorbent composed of a zeolite and the like into raw materials, removing the carbon dioxide generated at the time of foaming by adsorption onto the adsorbent, and as its result filling the foams with a fluorocargon gas and thereby improving heat insulating properties.
Now, a mechanism of the purification process of a fluorocargon gas in foams proposed by the above Japanese Patent Application Kokai (Laid-Open) No. 57-49628 is considered as follows. Thus, the adsorbent composed of a zeolite and the like selectively and preferentially adsorbs water before it adsorbs carbon dioxide, and hence water is immediately adsorbed by the adsorbent at the time of mixing the starting materials and the formation of carbon dioxide itself is prevented, in the reaction of water with a isocyanate by which the carbon dioxide gas is generated mainly. That is, even if an organic polyisocyanate to which a zeolite has previously been added is instantaneously mixed with a water-containing polyol component with an intention of foaming, the water has been already adsorbed by the zeolite in the time of the start of the foaming, so that the foaming takes place in the same manner as in the foaming process of a fluorocarbon alone. Further, although a carbodiimide reaction takes place to generate a slight quantity of carbon dioxide in the process of polymerization during the foaming, such a gas is readily adsorbed and as a result, the gas in the foams is purified and an excellent heat insulating performance is achieved.
According to Japanese Patent Application Kokai (Laid-Open) No. 57-49628, the main cause of CO.sub.2 formation is eliminated by dehydration and the slight quantity of CO.sub.2 formed by a carbodiimide reaction is also removed, whereby the gas in foams can be purified into a flon gas and heat insulating performance can be improved. However, from the standpoint of utilizing the carbon dioxide as a foaming gas, there is a problem that the quantity of the carbon dioxide formed was limited to that caused by a carbodiimide reaction and was so small in quantity that the quantity of a fluorocargon gas used could not saved greatly. In other words, the method of Japanese Patent Application Kokai (Laid-Open) No. 57-49628 was unable to simultaneously satisfy the two requirements of using carbon dioxide as a foaming gas and purifying the gas in foams into a fluorocargon gas, or the two problems of reducing the consumption of fluorocarbons for the purpose of solving the fluorocarbon problem and realizing a high heat insulation. Thus, it is an important problem to develop a technique therefor.